In other words, ADHD is no different than any other mental disorder, except that the drugs have effects people like, even if nothing's wrong with them.
If lumped all together, that seems to only help cause over-diagnosis (because the symptom list is so large) and makes it harder to study (because two very different conditions may be manifesting in very similar ways).
Additionally, people who may seem to have ADHD may in fact have OCD, anxiety, depression, or other disorders. And vice versa. Or they may have a combination of one or more of these with ADHD.
As someone outside all of this (I've never had to deal with it, so I only have a passing familiarity) it sounds like the term ADHD needs to be removed from use as it's only causing more confusion. The various facets should have their own name.